4 1/2 cups plums, pitted and chopped
1/2 cup water
7 1/2 cups sugar
1 (1.75-oz.) package powdered fruit pectin
8 half-pint canning jars with lids and rings
Sterilize and dry enough mason jars to store four pints of jam, and set aside. In a large pot, bring the plums and water to a boil. Reduce the heat to medium-low, cover, and simmer for 5 minutes. Stir in the sugar. Bring the mixture to a rolling boil over high heat, stirring constantly. Quickly mix in the pectin. Return to a boil, and boil for 1 minute, stirring constantly. Remove from heat. Skim off any foam that forms and discard. Wipe off the rims and run the spatula along the inside wall of the jar to let air bubbles escape. Place the metal lid and then screw on the band.
To preserve your jam for up to six months, process it by placing a wire rack in a deep pot, bringing the water to a boil, and boiling the jars for ten minutes. Carefully remove the jars and set them on a towel, allowing them to cool overnight. Check the lids to see if they sealed before storing in a cool place.